one of the leading causes of federal govt as follow
1.confederate vs unionist tug of war
2.Rapid expansion in the west and south and state's political configuration issue
3.issue of slavery in south vs north
4.political awareness among the masses
5.unequal wealth generation(since north was more progressive and generate more revenues they wanted to have greater contribution in legislation and executives,while south was uncompromising on particular issue)
6.organized and specialized departments for policing and defense purposes
7.spirit of federalism and territorization
8.Administrative reforms(like actions against kkk wouldnt be possible without
federal government initiatives

(from current perspective)
1.international surveillance and pretext for the creation of cia
2.democratic reforms (federal officers are responsible infront of congress)
3.implementation of legislation
you can deduce more importance by considering the following equation in mind
Federal government=congress+legislative+establishment+othe r working
bodies